Projection optical system and projection apparatus that enlarge and project an image displayed on a display

A projection optical system enlarges and projects an image displayed on an image display surface, the projection optical system comprising:

• a first optical system;
• and
• a second optical system, wherein
• the projection optical system is a monofocal lens or a zoom lens,
• the first optical system and the second optical system are arranged, in order starting with the first optical system, from an enlargement side of the projection optical system,
• the second optical system forms an intermediate image of the image between the first optical system and the second optical system,
• the first optical system enlarges and projects the intermediate image,
• the first optical system comprises:
• a first-A optical system and a first-B optical system in order from the enlargement side;
• and
• a reflecting optical element that bends a light path between the first-A optical system and the first-B optical system,
• the first-A optical system comprises:
• a negative front group comprising no positive lens;
• and
• a positive rear group comprising no negative lens,
• the light path is bent only once by 90 degrees, and
• the projection optical system satisfies formula (1):
• 0.2<Ta/Tw<0.3 (1)
• where Ta is an on-axis distance from a lens surface closest to the enlargement side to a lens surface closest to a reduction side in the first-A optical system, and Tw is an on-axis distance from a lens surface closest to the enlargement side to a lens surface closest to the reduction side in the projection optical system.